The essential role of the Y chromosome in primary male sex determination is well established and the gene that triggers this process is termed the testis-determining factor (TDF). The TDF locus has been mapped to the distal region of the short arm of the Y chromosome. A gene termed sex- determining region Y (SRY) has been cloned from this locus, and recent evidence indicates that SRY is indeed the TDF. The SRY gene is a member of a family of DNA binding proteins, termed the high mobility group (HMG). Hence, it is likely that SRY triggers testis determination by binding to specific DNA target sites. The physiologic binding site(s) of SRY in the human genome and the mode of action of SRY are unknown. However, studies of HMG proteins and their interaction with binding sites suggest that they influence gene transcription by changing the conformation of DNA. The principal hypothesis of this application is that the SRY gene product controls male sex determination by initiating activation of a cascade of genes. The long-term goal is the identification and characterization of the genes that interact with SRY and mediate testis determination. The specific aims are: l) To identify specific SRY binding sites in the human genome. 2) To determine the influence of the SRY protein on the conformation of the DNA of the SRY binding site. These studies will provide new information and create the foundation for future studies to examine the complex interplay of genes that are necessary for testis determination and differentiation. As DNA bending is an important biologic phenomenon, the information obtained from these studies may aid in the understanding of this complex process.